diff --git a/doc/changelog.rst b/doc/changelog.rst
index 624524f..e521b5c 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -7,6 +7,7 @@ Changelog
 Fixed
 ^^^^^
 - :class:`~scim2_models.ListResponse` pydantic discriminator issue introduced with pydantic 2.9.0. #75
+- Extension payloads are not required on response contexts. #77
 
 [0.2.1] - 2024-09-06
 --------------------
diff --git a/scim2_models/attributes.py b/scim2_models/attributes.py
index 7c665aa..3334165 100644
--- a/scim2_models/attributes.py
+++ b/scim2_models/attributes.py
@@ -85,7 +85,8 @@ def validate_attribute_urn(
     return f"{schema}:{attribute_base}"
 
 
-def contains_attribute_or_subattributes(attribute_urns: List[str], attribute_urn):
+def contains_attribute_or_subattributes(attribute_urns: List[str], attribute_urn: str):
     return attribute_urn in attribute_urns or any(
-        item.startswith(f"{attribute_urn}.") for item in attribute_urns
+        item.startswith(f"{attribute_urn}.") or item.startswith(f"{attribute_urn}:")
+        for item in attribute_urns
     )
diff --git a/scim2_models/base.py b/scim2_models/base.py
index 04fccaf..3814870 100644
--- a/scim2_models/base.py
+++ b/scim2_models/base.py
@@ -700,7 +700,10 @@ def get_attribute_urn(self, field_name: str) -> str:
         """
         main_schema = self.model_fields["schemas"].default[0]
         alias = self.model_fields[field_name].serialization_alias or field_name
-        return f"{main_schema}:{alias}"
+
+        # if alias contains a ':' this is an extension urn
+        full_urn = alias if ":" in alias else f"{main_schema}:{alias}"
+        return full_urn
 
 
 class ComplexAttribute(BaseModel):
diff --git a/scim2_models/rfc7643/resource.py b/scim2_models/rfc7643/resource.py
index 643143a..fe87007 100644
--- a/scim2_models/rfc7643/resource.py
+++ b/scim2_models/rfc7643/resource.py
@@ -136,7 +136,6 @@ def __new__(cls, name, bases, attrs, **kwargs):
                 schema = extension.model_fields["schemas"].default[0]
                 attrs.setdefault("__annotations__", {})[extension.__name__] = Annotated[
                     Optional[extension],
-                    Returned.always,
                     WrapSerializer(extension_serializer),
                 ]
                 attrs[extension.__name__] = Field(
diff --git a/tests/test_resource_extension.py b/tests/test_resource_extension.py
index 33373ea..ea7bcb3 100644
--- a/tests/test_resource_extension.py
+++ b/tests/test_resource_extension.py
@@ -257,3 +257,27 @@ def test_extensions_schemas():
         ],
         "userName": "foobar",
     }
+
+
+def test_validate_items_without_extension():
+    """A model with an optional extension should be able to validate a payload
+    without an extension payload.
+
+    https://github.com/yaal-coop/scim2-models/issues/77
+    """
+
+    payload = {
+        "schemas": ["urn:ietf:params:scim:schemas:core:2.0:User"],
+        "id": "new-user",
+        "userName": "new-user@example.com",
+        "meta": {
+            "resourceType": "User",
+            "created": "2010-01-23T04:56:22Z",
+            "lastModified": "2011-05-13T04:42:34Z",
+            "version": 'W\\/"3694e05e9dff590"',
+            "location": "http://localhost:46459/Users/new-user",
+        },
+    }
+    User[EnterpriseUser].model_validate(
+        payload, scim_ctx=Context.RESOURCE_CREATION_RESPONSE
+    )